1. Field of the Invention
The present invention relates generally to a transceiver of a wireless communication system and, more particularly, to a transceiver having a multistage channel filter in a wireless communication system.
2. Description of the Related Art
The Long Term Evolution (LTE) specification of the 3rd Generation Partnership Project (GPP) defines multiple channel bandwidths including 20, 15, 10, 5, 3 and 1.4 MHz, and requires support for these channel bandwidths.
For multiple channel bandwidths in LTE, a transmitter unit (Tx) must satisfy very stringent requirements, including spectral masking. A receiver unit (Rx) must also satisfy very stringent requirements including high levels of adjacent channel selectivity and channel blocking with regard to interference signals from adjacent channels.
It may be highly uncompetitive to develop and employ separate transceivers for individual channel bandwidths in consideration of many nations and network operators. Hence, in practical situations, Radio Frequency (RF) filters and analog Intermediate Frequency (IF) filters are to be designed in accordance with the widest channel bandwidth of 20 MHz. At the same time, these RF filters and analog IF filters are adapted through digital channel filters to support the narrower channel bandwidths provided in the LTE specification and requirements of various nations and/or operators.
A digital channel filter may perform very steep filtering at the edge of a channel bandwidth, which may be difficult to achieve using an analog channel filter.
As the channel bandwidth narrows, the number of taps required in a digital channel filter increases. For example, the number of filter taps (i.e., coefficients) required for 5 to 1.4 MHz may be four to eight times that of the number of filter taps required for 20 MHz. Implementing a digital channel filter having a large number of taps requires a large number of multipliers. The multiplier is one of the most complex computational components in digital hardware. Therefore, it may be not advantageous to implement a digital channel filter using a large number of multipliers.